1. Field of the Invention
The present invention relates to selective catalytic alkylation, e.g., propylation, of aromatic hydrocarbons, e.g., benzene, using olefin mixtures containing both ethylene and propylene.
2. Description of the Prior Art
Alkylation of aromatic hydrocarbons with olefinic alkylation agents in the presence of zeolite catalysts such as ZSM-12 is known in the art. U.S. Pat. No. 3,755,483, issued Aug. 28, 1973 to G. T. Burress, for example, discloses that aromatic hydrocarbons such as benzene and toluene can be usefully alkylated either with ethylene or with propylene, in the vapor phase in the presence of ZSM-12 zeolite catalyst.
In commercial practice, however, alkylating agents comprising only one alkylating olefin such as pure ethylene or pure propylene are relatively expensive to obtain. Sources of olefin alkylating agents, for example, include refinery off-gases or tail gases which are streams containing dilute concentrations of mixtures of both ethylene and propylene and possibly higher olefins. A more common source of mixed ethylene/propylene feedstocks is the effluent produced by the thermal cracking of hydrocarbon streams in olefin production operations. Such a cracking product is generally much higher in mixed olefin content than are refinery off-gases. When such mixed olefin-containing gas streams from whatever source are used to alkylate aromatic compounds, a mixture of several types of alkylated aromatic products is frequently produced. For example, Zavgorodnii et al; Izvest. Vysshikh Ucheb. Zavedenii, Khim. i Khim. Tekhnol., Vol. 4, No. 1, pp. 128-132 (1961), and Lebedev et al; Khim. Prom. (Moscow), Vol 47, No. 10, pp. 744-746 (1971), both report the alkylation of benzene with gas streams containing ethylene and propylene over AlCl.sub.3 and BF.sub.3.H.sub.3 PO.sub.4 catalysts to provide a product comprising both ethylbenzene and isopropylbenzene.
Attempts have been made to selectively provide a single alkylated aromatic product in processes utilizing mixed ethylene/propylene streams as the alkylating agent. U.S. Pat. No. 3,086,998; Issued Apr. 23, 1963 to G. L. Hervert, for example, discloses a process whereby propylated aromatic hydrocarbons can be selectively formed by using a boron trifluoride/modified sulfur-containing alumina catalyst to promote aromatic alkylation with an olefin mixture containing both ethylene and propylene. Notwithstanding such efforts, there is a continuing need to identify additional catalysts and catalyst systems which can be usefully employed to provide processes for the selective production of propylated aromatic compounds such as cumene using readily available, low cost ethylene/propylene streams as the alkylation agent.